1. Field of the Invention
This invention relates to apparatus and methods for soldering straps to terminals of electric dry cells for fabricating dry cell batteries. In particular, the invention relates to the use of microwave induction or R F induction heating for connecting, both physically and electrically, a plurality of electric dry cells for forming a dry cell battery.
2. Prior Art
In the field of toys, radio controlled toys, such as self propelled, remote controlled airplanes, boats and land vehicles such as cars, trucks and other vehicles, for example, have become very popular. Them vehicle has its own power plant which is usually in the form of a gasoline engine or an electric motor. When electric motors serve as a power plant for such toy vehicle, the onboard power supply or ‘fuel’ is usually a rechargeable, interchangeable electric battery of the dry cell type. The rechargeable, interchangeable electric dry cell battery is a fabrication of several connected electric dry cells, normally referred to as ‘dry cells’. The dry cells are coupled together both electrically and physically, made as compact as technology allows.
In fabricating an electric battery from a plurality of electric dry cells a strap of highly conductive material in the form of a strap, for example, is connected, usually by soldering, to the terminals of adjoining electric dry cells. Contemporary methods used for fabricating a rechargeable electric dry cell battery from a plurality of rechargeable electric dry cells includes the use high temperature conduction or ‘hot-tip’ soldering, flame generated heat soldering or welding, which heats the connection strap and the terminal to which the strap is to be soldered to an high elevated temperature so as to melt soldering material at the connection between the terminal and the connection strap. Often the use of hot-tip soldering or conduction causes problems not apparently visible. It is well known that heat is an enemy of electric dry cells. Heat destroys the chemical balance in the electrolyte matter in the dry cells and drives the electrolyte matter, and hence the dry cell into deterioration. When hot-tip soldering is used to solder a connection strap to a terminal of a dry cell, a film of solder is often applied to the under side of the end section of the strap which will be connected to the terminal. In order to effectively solder-connect the two pieces, the two pieces must be in physical contact during the soldering effort. This requires that the hot-tip of the soldering tool must be placed in contact with some other part of the strap. From a practical standpoint, the hot tip of the soldering tool is placed in contact with the upper side of the strap, above where the strap and the terminal are placed into contact. This requires that the high heat or energy, at the tip of the soldering tool, be transferred to the outer side of the strap, travel through the thickness of the strap, through the solder between the strap, be transferred to the terminal at the junction with the strap and heat the terminal of the cell at least to a temperature sufficiently high to be acceptable to receive the heat liquified solder. It becomes obvious that at least some of the heat energy is wasted and that some parts of this combination are heated much more than other parts. If the cell terminal, which is driven to the lowest heat level of the connecting pieces, is not heated to a high enough level the solder connection will fail. If the cell terminal is heated to an excessively high level, the heat in the terminal will adversely affect the electrolytic matter in the cell and drive the cell to early deterioration, shortening the life of the cell and the battery of which it is a part.
It becomes apparent that the quantity of heat actually applied to the outer side of the strap during the soldering effort is greatly in excess of the heat required to raise the temperature of the terminal to a degree where the terminal is in a condition to accept the solder so that the terminal and the strap may be physically and electrically connected by the solder. Because much heat applied to the outer side of the cell strap in the hot-tip soldering process is lost by absorption by the strap components, the solder, by transfer of heat and by the terminal components, fabrication of dry cell batteries from a plurality of electric dry cells is expensive.
A welding tool has been used as the primary source of heat for spot welding a strap to the terminal of a dry cell for fabricating a dry cell battery. However, the use of spot welding in the fabrication of dry cell batteries has been found unreliable because a spot weld contact is not an excellent electric conductor, which is needed for the rapid discharge to which the batteries are subjected when the battery is used to power an electric motor in a toy vehicle, when racing the vehicle. The unacceptability of the single spot weld connection between a cell strap and the terminal of a dry cell battery lead to the use of additional spot welds, for example to the use of an average of five spot welds. The increase in the number of spot welds to such a small area became destructive to the strap and very costly. Also when spot welding a cell strap to a terminal of a dry cell, an electric charge is the vehicle that generates the heat for the welding. The electric charge driven through the dry cell for the spot welding has an adverse effect on the chemical electrolyte material in the dry cell that stores electric energy. One driving charge is a commercially acceptable adverse effect but multiple driving charges from a plurality of closely applied spot welds on the same small area, have an unacceptable adverse effect on the life of the dry cell, which translates into an unacceptable adverse effect on the life of the battery of which the dry cell is a part.